The Recovery of Valuable Vapour Phase Solvents using Activated Charcoal Cloth

Abstract

The removal of toluene and perchlorcethylene vapours from air by adsorption onto activated charcoal cloth and their subsequent recovery by regenerating the cloth with low pressure steam was investigated. Additionally, present market areas for activated charcoals have been presented as well as outlining new market fields for activated charcoal cloth. The potential of charcoal cloth for use on solvent recovery plants has been assessed using both batch and continuous equipment. The charcoal cloth which on average measured 0.72m by 0.6m and weighed 0.045Kg was wound on a former and placed in a glass column for the batch operations. The experimental results in general could be represented by Langmuir isotherms and the maximum adsorbate-adsorbent mass ratios obtained were, 0.830 for perchlorcethylene and 0.388 in the case of toluene. An approximate working charge of 52% corresponding to a steam-solvent mass ratio of 2.5 was measured for both solvents. Cyclic efficiencies were evaluated at 45.8% and 24.2% for the chlorinated solvent and toluene respectively. Empirical equations used to describe the equilibrium relationships and the adsorption waves were computed and are presented. The experimental apparatus constructed for the continuous operations basically consisted of four sections; an air solvent mixing region, the adsorber, regenerator and solvent recovery unit. A continuous length of cloth was transported over a series of rollers through a 1m length of duct counter currently to the flow of solvent vapour-air mixture. The cloth was then passed through the regenerator where solvent was desorbed by steam. Measurements of the cloth's residual activity showed an immediate drop after one regeneration, but then remained fairly constant with increasing number of regenerations. Evidence in this thesis exists to show that at present activated charcoal cloth would be uneconomical for the batchwise recovery of solvents and more development work has to be carried out before the cloth can be established as an effective material for the continuous recovery of solvent vapours. However, it is demonstrated that charcoal cloth can be beneficial in numerous other areas.